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Income Taxes (Carry Overs) (Details) - CAD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017
Tax Loss Carry Forwards [Abstract] |  |
Deferred Tax Assets, Tax Credit Carryforwards | $ 269 | $ 314
Tax Loss Carry Forwards Valuation Allowance [Abstract] |  |
Deferred Tax Assets, Valuation Allowance | 163 | 105
Capital Loss Carryforward [Member] | Canada Revenue Agency [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross Tax Carryforwards, Tax credit / capital loss | 86 |
Unrecognized amounts, Tax credit / capital loss | (77) |
Tax credit carryforwards, NOL / capital loss | 9 |
Capital Loss Carryforward [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross Tax Carryforwards, Tax credit / capital loss | 6 |
Unrecognized amounts, Tax credit / capital loss | (6) |
Tax credit carryforwards, NOL / capital loss | $ 0 |
Capital Loss Carryforward [Member] | Minimum [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2019 |
Operating Loss Carryforward [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross Tax Carryforwards, Tax credit / capital loss | $ 34 |
Unrecognized amounts, Tax credit / capital loss | (34) |
Tax credit carryforwards, NOL / capital loss | 0 |
Operating Loss Carryforward [Member] | Canada Revenue Agency [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross Tax Carryforwards, Tax credit / capital loss | 817 |
Unrecognized amounts, Tax credit / capital loss | (405) |
Tax credit carryforwards, NOL / capital loss | 412 |
Operating Loss Carryforward [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross Tax Carryforwards, Tax credit / capital loss | 2,848 |
Unrecognized amounts, Tax credit / capital loss | 0 |
Tax credit carryforwards, NOL / capital loss | $ 2,848 |
Operating Loss Carryforward [Member] | Maximum [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2025 |
Operating Loss Carryforward [Member] | Maximum [Member] | Canada Revenue Agency [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2038 |
Operating Loss Carryforward [Member] | Maximum [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2037 |
Operating Loss Carryforward [Member] | Minimum [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2019 |
Operating Loss Carryforward [Member] | Minimum [Member] | Canada Revenue Agency [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2027 |
Operating Loss Carryforward [Member] | Minimum [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2024 |
State Operating Loss Carryforward [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross Tax Carryforwards, Tax credit / capital loss | $ 1,314 |
Unrecognized amounts, Tax credit / capital loss | (47) |
Tax credit carryforwards, NOL / capital loss | $ 1,267 |
State Operating Loss Carryforward [Member] | Maximum [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2038 |
State Operating Loss Carryforward [Member] | Minimum [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2024 |
Tax credit carry forwards [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross Tax Carryforwards, Tax credit / capital loss | $ 268 |
Unrecognized amounts, Tax credit / capital loss | 0 |
Tax credit carryforwards, NOL / capital loss | $ 268 |
Tax credit carry forwards [Member] | Minimum [Member] | US Tax authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Expiration period, Tax credit / capital loss | 2019 |
Domestic Tax Authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross tax carry forwards, NOL | $ 33 | 40
Foreign Tax Authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross tax carry forwards, NOL | 0 | 194
Other Tax Authority [Member] |  |
Tax Credit Carryforward [Line Items] |  |
Gross tax carry forwards, NOL | $ 1 | $ 0

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- Definition Amount, before allocation of a valuation allowances, of deferred tax assets attributable to deductible tax credit carryforwards including, but not limited to, research, foreign, general business, alternative minimum tax, and other deductible tax credit carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319 + Details
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